Questions I

So, already some questions! Thanks Mark and Mom. The questions and my answers are after break. As a disclaimer, which really should go in the about this blog box, all answers are to the best of my knowledge, and therefore might be a little off.

What are gluons composed of?
Well, the current thought is that gluons are one of about 16 fundamental particles. The Standard Model of Physics theorizes that there are 3 fundamental types of particles: quarks, leptons (things like electrons), and bosons. As one of the bosons, the gluon is thought to be just itself. While protons and neutrons are composite particles (they have some sort of internal structure), their constitutents are currently thought to be made up of nothing else. So, the up quark is just an up quark, it's composed only of matter, same with the down quark, and with gluons. It's just a tiny little bit of stuff.
If you like string theory, where everything is built up from one-dimensional strings, a gluon is a fundamental resonance of the string. If the strings were guitar strings, a gluon and a quark would both be different notes of the same string.

How did gluons come to be discovered?
When particles are collided in an accelerator, one of the clearer signals that can come out is a so-called hadron jet: a cone filled with hadrons. This happens because quarks hate being alone. Whenever physicists try to isolate a quark, the gluons that bond it to the other quarks begin to stretch. More and more energy has to be put into the bond to isolate the quark, and eventually, so much energy is in the bond that it forms two new quarks, and the quark you were trying to isolate pops off your old particle with a new friend.
To satisify various forms of conservation, quarks are made in pairs, so if we have an even number of jets, there from the pair of quarks. If we have an odd number of jets, there had to be some other particle involved, that also tends to form hadrons rather than existing freely. Theorists tell us that gluons satisfy those requirements. Much like quarks can't exist freely and independently, neither can gluons, so they also produce jets when they are involved in collisions.